Crystalline colloidal arrays have been used for a variety of purposes. A crystalline colloidal array (CCA) is a three-dimensional ordered array, typically produced from monodispersed colloidal particles, which may be composed of inorganic or organic materials. Such CCAs are often provided in a hexagonal close-packed (HCP) or random hexagonal close-packed (RHCP) structure, exhibiting a layered structure with a preferred diffraction axis that is perpendicular to the layers in the structure. The diffraction wavelength varies with the angle of incidence to these layers. When fixed in a binder as a colorant, such CCAs can diffract radiation in the visible spectrum. These colorant CCAs exhibit a goniochromatic effect when applied to a substrate.
When used in a film or coating, the CCAs typically are oriented predominately in a single direction, such as with the hexagonal planes of the CCAs positioned parallel to the surface of the film or substrate. More recently, CCAs have been used to create unique optical effects, such as for producing images or to function as sensors.